Drug delivery devices for setting and dispensing a single or multiple doses of a liquid medicament are as such well-known in the art. Generally, such devices have substantially a similar purpose as that of an ordinary syringe.
Drug delivery devices, in particular pen-type injectors have to meet a number of user-specific requirements. For instance, with patient's suffering chronic diseases, such like diabetes, the patient may be physically infirm and may also have impaired vision. Suitable drug delivery devices especially intended for home medication therefore need to be robust in construction and should be easy to use. Furthermore, manipulation and general handling of the device and its components should be intelligible and easy understandable. Moreover, a dose setting as well as a dose dispensing procedure must be easy to operate and has to be unambiguous.
Typically, such devices comprise a housing or a particular cartridge holder, adapted to receive a cartridge at least partially filled with the medicament to be dispensed. They further comprise a drive mechanism, usually having a displaceable piston rod which is adapted to operably engage with a piston of the cartridge. By means of the drive mechanism and its piston rod, the piston of the cartridge is displaceable in a distal or dispensing direction and may therefore expel a predefined amount of the medicament via a piercing or needle assembly, which is to be releasably coupled with a distal end section of the housing of the drug delivery device.
The medicament to be dispensed by the drug delivery device is provided and contained in a multi-dose cartridge. Such cartridges typically comprise a vitreous barrel sealed in distal direction by means of a pierceable seal and being further sealed in proximal direction by the piston. With reusable drug delivery devices an empty cartridge is replaceable by a new one. In contrast to that, drug delivery devices of disposable type are to be entirely discarded when the medicament in the cartridge has been dispensed or used-up.
With such multi-dose drug delivery devices at least a last dose limiting mechanism is required to inhibit setting of a dose exceeding the amount of medicament left in the cartridge. This is to avoid a potentially dangerous situation for the user believing that a dose actually set is entirely injected.
There already exist some drug delivery devices with end of content mechanisms or last dose mechanisms. Most of these mechanisms require a rather complicated interaction of components of a drive mechanism. Typically, a separate last dose limiting member is required that successively propagates either in distal or proximal direction every time a dose is set or dispensed. When reaching an end of content configuration, a last dose limiting member typically engages with a corresponding stop to inhibit a further dose incrementing operation or actuation of the delivery device.
Numerous last dose limiting implementations are non-visibly integrated somewhere in the drive mechanism of such drug delivery or injection devices. A user not being aware that the content of a cartridge is almost used up may be fairly surprised or confused when being suddenly confronted with an end of content situation. In circumstances in which the residual amount of medicament left in a cartridge is smaller than a prescribed dose to be administered the user may be in need of a spare cartridge. However, when being unaware, that such an end of content situation is likely to occur, a new cartridge may be unavailable to the user when the end of content is actually reached.